Semiconductor structure and method of forming the same

Abstract

A semiconductor structure and a method for forming the same are provided. The semiconductor structure includes: a substrate; a fin structure protruding from the substrate, the fin structure extending along a first direction; isolation features disposed on both sides of the fin structure; a gate structure over the fin structure and extending on the isolation features along a second direction perpendicular to the first direction; and wherein the gate structure includes a first segment and a second segment, the second segment being over the first segment and including a greater dimension in the first direction than that of the first segment.

What is claimed is: 
     
       1. A method for forming a semiconductor structure comprising:
 forming a fin structure along a first direction on a semiconductor substrate; 
 depositing a first layer over the semiconductor substrate and the fin structure by growing a group III or group V element-doped silicon; and 
 depositing a second layer over the first layer by growing a carbon or nitrogen-doped silicon; and 
 patterning the first layer and the second layer to form a dummy gate stack occupying a gate region over the fin structure and extending along a second direction perpendicular to the first direction. 
 
     
     
       2. The method of  claim 1 , wherein the group III element comprises boron. 
     
     
       3. The method of  claim 1 , wherein a concentration of the group III or group V element in the first silicon layer ranges from about 1E19 to about 1E22 atoms/cm 3 . 
     
     
       4. The method of  claim 1 , wherein the temperature and the pressure used for depositing the first layer and the second layer are substantially the same. 
     
     
       5. The method of  claim 1 , further comprising oxidizing the first layer and the second layer of the dummy gate stack. 
     
     
       6. The method of  claim 5 , wherein the oxidizing is performed under a pressure ranging from about 2 to about 100 torr. 
     
     
       7. The method of  claim 1 , wherein the oxidation rate of the first layer is greater than that of the second layer. 
     
     
       8. The method of  claim 5 , further comprising removing an un-oxidized portion of the dummy gate stack. 
     
     
       9. A method for forming a semiconductor structure, comprising:
 forming a fin structure along a first direction on a semiconductor substrate; 
 depositing a first layer over the semiconductor substrate and the fin structure by growing a group III or group V element-doped silicon, the first layer having a first oxidation rate; 
 depositing a second layer over the first layer by growing a carbon or nitrogen-doped silicon, the second layer having a second oxidation rate; wherein the first oxidation rate is greater than the second oxidation rate; and 
 oxidizing the first layer and the second layer; and 
 removing an un-oxidized portion of the first layer and an un-oxidized portion of the second layer. 
 
     
     
       10. The method of  claim 9 , further comprising:
 patterning the first layer and the second layer to form a sidewall over the fin structure, extending along a second direction perpendicular to the first direction; and 
 wherein the oxidizing the first layer and the second layer comprises oxidizing from the sidewall. 
 
     
     
       11. The method of  claim 10 , wherein the oxidizing is performed under a pressure ranging from about 2 torr to about 100 torr. 
     
     
       12. The method of  claim 9 , wherein the first layer is formed by depositing a silicon layer in-situ doped with a group III or a group V element. 
     
     
       13. The method of  claim 9 , wherein the first layer is formed by:
 depositing a silicon layer; and 
 implanting the silicon layer with a group III or a group V element. 
 
     
     
       14. A method for forming a semiconductor structure, comprising:
 forming a fin structure along a first direction on a semiconductor substrate; 
 depositing a first doped layer over the semiconductor substrate and the fin structure by growing a boron-doped silicon; 
 depositing a second doped layer over the first layer by growing a carbon or nitrogen-doped silicon, and 
 patterning the first doped layer and the second doped layer to form a dummy gate stack occupying a gate region over the fin structure, extending along a second direction perpendicular to the first direction, the dummy gate stack having a sidewall. 
 
     
     
       15. The method of  claim 14 , wherein the first doped layer is in-situ doped with boron within a range of from about 1E19 to about 1E22 atoms/cm 3 . 
     
     
       16. The method of  claim 14 , further comprising:
 oxidizing the first doped layer and the second doped layer from the sidewall. 
 
     
     
       17. The method of  claim 1 , further comprising:
 removing a portion of the dummy gate stack by a plasma etch operation. 
 
     
     
       18. The method of  claim 9 , wherein the removing the un-oxidized portion of the first layer and the un-oxidized portion of the second layer comprises a plasma etch operation. 
     
     
       19. The method of  claim 8 , wherein the removing the un-oxidized portion of the dummy gate stack exposes a surface of the fin structure. 
     
     
       20. The method of  claim 19 , further comprising forming a high-K dielectric layer on the surface of the fin structure.